Pipe, tube and hose couplings of many types have been provided heretofore and a recognition of the problems involved in the design, production and use of such coupling requires a brief review of the several types. Perhaps the most common type of couplings for disconnectable or replaceable purposes is the screw-type coupling in which a pair of threadedly interconnectable members form a union when the nut portion of one is screwed onto the male portion of the other. In this coupling, the axially aligned coupling members may be provided with mutually engaging transverse faces of complementary configuration and the nut may be rotatably mounted on one coupling member and may have an inwardly turned annular flange bearing against an axial shoulder of this coupling member. A simpler connection makes use of a threaded sleeve between a pair of male threaded members, this system having the disadvantage that one of the members must be rotated through several turns at least in order to ensure a proper tight fit. A seal is guaranteed by using so-called taper or pipe threads. These systems have the disadvantage that rotation of one member relative to the other may not always be possible, that threads are highly sensitive to the presence of foreign matter and to damage, that the threads may not be cut accurately in the first instance, and that the stress applied to the threads in the axial direction may strip them. Accordingly, these techniques have not been fully successful for pipes of materials other than metals.
In the flange coupling, two pipe members are axially aligned and may be provided with integral or dismountable flanges which are bridged by screws or bolts securing the pipes in axial alignment. Such systems are prone to damage by transverse stresses, frequently require considerable time for assembly of the joint since a number of threaded members are provided, and may not be suitable for certain materials in which the stress applied to the flange may be sufficient to break it.
Various clamp-type couplings have also been provided heretofore, generally for the rapid connect and disconnect coupling of flexible hose to withstand low or high pressures. This system generally comprises a pair of axially interfitted coupling members and a clamp means for securing them in axial alignment. The clamp means may consist of hook-type members which are deflected upon insertion of one member into the other and re-engage to prevent withdrawal of the two members unless a detent is operated to permit such withdrawal. These systems have the disadvantage of complex construction and are assembled from parts which are not amenable to production by conventional techniques such as molding.
Finally, I may mention wedge-type couplings in which the relative rotation of two parts of a coupling member, by screw thread or cam systems shifts a wedge element axially to clamp against the exterior of an inner member. This system has similar disadvantages to those given above.
In summary, prior-art systems for coupling two pipes, tube or hose sections together, for connecting a tube, pipe or hose section to another fitting, or for joining two fittings have been characterized by problems in resisting transverse stress, in possessing an excessive number of parts, of requiring moving parts which may be readily damaged or not conveniently manufactured, or requiring excessive manipulation, and of being of inordinate complexity. As a consequence, many attempts have been made to modify one or another of these coupling systems to overcome the disadvantages, these attempts being likewise without success.
I may mention specifically the systems which have been generally described above as providing hooks or clips which engage when two members are urged axially together and may be secured by some retaining element or ring thrust over these clips. The hooks cannot withstand significant transverse stress and even when they may be conveniently manufactured from a synthetic resin, are difficult to handle and manipulate. More often than not, such hook-type couplings or couplings provided with axially interengaging formations are difficult to handle.